Recuperator means for combustion furnaces



Jan. 16, 1951 H. Escl-IER. 2,538,446

RECUPERATOR MEANS FOR COMBUSTION FURNACES Filed Dec. 27, 1944 4 Sheets-Sheetl l Jan. 16, 1951 H. Escl-1ER 2,533,446

RECUPERATOR MEANS FOR CGMBUSTION FURNACES Filed Dec. .27, 1944 4 sheets-sheet 2 4 Sheets-Sheet 5 H. ESCHER RECUPERATOR MEANS FOR COMEUSTION FURNACES Jan. E6, 1951 Filed Deo. 27, 1944 Il?, U ein/@01 Jan. E6, E951 H. ESCHER RECUPERATOR MEANS FOR COMBUSTION FURNACES 4 sheets-sheet 4 Filed Dec. 27, 1944 Patented Jan. 16, i951 Y RECUPERATOR MEANS FOR lCQMBUSTIION FURNAoEs `Hans Escher, Wollongong, New South Wales,

Australia, assigner to Australianlronztecl Limited, Sydney,ll\lew South ,Wales Australia, a company of New `South Wales Y 1 Application This invention relates to combustion furnace recuperators for heating air orother gases or `gas mixtures bydheat exchangev between the gas to bev heated and the products ofcrcombustion eX- `hausting from the furnace. The inventionv is particularly applicable toY high temperature furnages such as those usedcforrmectal meltingLand4 glass andsteelwmanufracturing purposes. v Recuperators are'knrown'in which themain s treamof flue gases is divided into a number of smaller streams in order to obtain satisfactory heat transfer from the flue Agases to the' gas or air"to be heated by direct contact between the gases and the partitions dividing the flue gas stream.r Frictional losses are :high in such arrangements, both for the flue gases and they gas or air to be heated gheat transfer is not efficient, owing to the uneven distribution of gases in the various passages, whichis further aggravated by clogging of the passages vin operation, and a large proportion of the heat transfer'bsurfaces are inaccessible for inspection,cleaning and repairs.

According' tothe present invention lthe above disadvantages are avoided by making use of the heat radiating power of the flue gases and sus# pended particles. Heat radiation from ue gases containing carbon dioxide, watervapour, fumes and suspended particles increases rapidly with increasing temperature thereof, and, accordingly, the recuperator of this invention offers particular advantages in just thosecases, namelywhere the ilue gases from high temperature furnaces are to be used,'where theprior art recuperators are most inefficient.

The objects of this inventioninclude the pro? vision in a recuperator, of means whereby a subpassage, and the said gas or air is distributedl substantially-uniformly through the gasheating passage. .f Y f, Y

The above and other lobjects of thisA invention are achieved by employing a large substantially unobstructed conduit betweenV the recuperatorentrance and outlet forthevflue gases, by surrounding the conduit by va shell spacedV close thereto to define a gas heating passage, and by December-27, 1944,'seria1N0. 570,02 in Australia April/4,1944

surrounding the ends or Athe shell by gas inlet' and outlet. boxes. The inletand outlet boxes enable 'une zas or all' 'to ce heated to fue distributed stantial portion'oi the :heat transfer from the flue sucstantiaLy uniformly to the gas ncatmg passaga'and furthermore allow pressure losses au the ends or' 'one gas heating passage to be reduced by fiaring the endsoofk the shell outwardly in the boxes. l

:1 Itis a further objectto provide for expansion due t0 temperature changes without unduly reducing une rigidity or une lecuperatcr. lo enact this object the inlet` and/or outlet boxes and/or outer shell are made suilicently flexible to allow,

for v'such expansion. The said expansion may bef employed to' control the flow of` cooling gases to Y ne recuperator.

havingrinlet and outlet boxes for the gas to be` preheated in which the parts of the conduit enciosed by the boxes are as errective for hearl tr ansfer-as the rest Vof the heating surface of the conduit. To effect this o bJect the ends of the Snell are extendedffor substantial distancesinto the boxes, and preferably have flared ends to reduce pressure losses and to efect a better distribution of the gas to be preheated.

The recuperator of the present invention allows high preheat temperatures to be obtained with less `dangerof Ylocalised overheating than with other types using individual tubesof small diameter.f -Hot spots areV automatically equalised by radiation interchange Within the conduit and to the outer shell and by sideways transfer through the heating surface of the conduit itself. With this construction the flue gases can be guided centrally so thatv they do not impinge at right angles against a section of the heating surface, thus reducing the possibility of hot spots, and allowing very high temperatures of the flue gases well above the allowable safe working temperature of the materials used in the construction of the recuperator.

The-present invention consists in a combustion furnace recuperator, comprising a conduit which has an entrancey end adapted to receive flue-gas exhausting from the flue-gas outlet of a furnace,

air supply'being interrupted, to relieve the'ove'rvdissipating fins 45 thereon) is unlagged, and that the inlet box I is also unlagged. These unlagged parts are situated on the coolerside of plane I2 which (as already stated herein) may be'regardved as defining the cooler end of the radiant heating zone.Y Becauseof this,.under normal operating temperatures, the heat loss by radiation to ratmosphere from the unlagged parts` is practically negligible. When, however, the flue-gas tempera--v tures rise appreciably above normal, the radiant heating zone may be said to extend towards .the

lconduit Vend l0,.and in that event the unagged parts soon become effective radiators. The. more .the flue-gas temperature rises thevery much greater does the radiating ability of the unlagged `surfaces become (the radiation being proportional vvto the absolute temperature raised to the fourth power) and consequently the cooling eiect thus automatically obtained, rapidly negatives overheating and rapidly dies away when-normal fluegas temperatures again prevail.

The construction shown in Fig. 1 illustrates further cooling .devices which whileA shown in supplement to the radiation cooling means just previously described, may be employed in'substitution therefor. These further co-oling devices enable a stream of cooling'uid (such asair) to be directed as a cool diluent into the flue-gas issuingl from the furnace,`and/or into heateX-V change relationship with the exterior of `theshell The further cooling devices comprise a jacket casing 4l forming a cooling trunk having one end 42 open to atmosphera'and the other end k43 open to an air feed pipe 44.

A second air feed pipe 45 opens to the furnace flue duct 45 leading to outlet 3. The two feed pipes 44 and Yd5 .branch into an air duct 4l which includes a control valve 48'. Duct-4l is connected to an air pump or other source of air under pressure. If the recuperator is being used for the preheating of air, the duct 4l may be branched into the feed pipe 32, as indicated by dotted lines at 49, so that the pump 31 may then become the source of both feed air and cooling air. Y Y

The feed pipes 44 `and 45 .are preferably equipped with valve devices (such as ap. valve indicated at 55) wherebythe air output of duct 41 may be allocated to the feed .pipes in selected proportion, or directed into either one of these pipes to the exclusion of the other; It' follows from this, that` if desired, the integers herein numbered 4E to `'i4 maybe omitted `from the constructiomand in such case air cooling may be effected entirely by dilution of flue-gas, with cool air, by way of duct 4l and feed pipe 45.. Alternatively, the pipe 45 may beomitted or blankeol 01T, and insuch case air cooling may be effected entirely by means of the duct 4l and the integers 4l to 44. Y K

The valve 48 may Vbe operated 'manually or otherwise. For preference it is automatically operable in response to longitudinal extension of the conduit z5 as a result of expansion due to overheating. To this end a' bracket 5I isV fixed relative to the conduit, and this bracket is equipped with a` pull rod 52 which engagesa bell crank 53 fulcrumed at 5t. VThe bell crank engages a head 55 on the stem'o-f v'al`v148--and said valve is spring loaded as indicated'at 55. orfby 6 extends by expansion, the bracket 5l, pull rod 52, bell crank 53.A and head 55 operate the open valve 48. When the conduit contracts the spring 56 or dead weight recloses valve 48.

Althoughin Fig. 1 the recuperator is shown to be disposed about a horizontal axis, it will be appreciated that the recuperator may be disposed vertically or otherwisenon-horizontally.

Figs. 2 and '3 illustrate vertically disposed recuperatoruwhich, as previously/indicated herein, is Vsuitable'for a furnace the flue-gases'of which issue at relatively low temperature.

' The conduit' (indicatedrgenerally by numeral 5'!) has its entrance end 58 adapted to receive hot nue-gas from the flue-gas outlet 59 of a furnace, a part of which is indicated at 5S.

other end 6l of the conduit islin direct communication with atmosphere and is furnished with a movable cover 62 of conventional type. kThe internally unobstructed radiation zone formed by a part of the conduit 57 is indicated by span 53. It will. be appreciated Ythat in any of the embodiments of the invention described herein, it is not intended that the indicated cooler-end limits of the several radiation zones be regarded as fixed planes beyond which no radiation occurs, but rather as vicinities beyond which recovery of heat-by radiation ceases to be more efficient,

or markedly more efficient, than recovery of avail--Y able heat by direct contact of flue-gas with the conduit inner surface. This lack of distinctness in the cooler-end limit of the radiation zone is particularly present in the recuperator construction subject of Figs. 2 and 3, owing to the relatively small difference between the flue-gas temperatures obtaining at the endsV 58 and 6l. Because` of this it may be noted that while appreciable radiation may occasionally or Veven frequently occur beyond the cooler-end Vof span 53, the said span represents a conduit Zone in which, under normal working conditions, economically advantageous radiation will invariably take place,

and that beyond the coolernend vof span 53 theV said span represents a conduit zone in which, under 'normal working conditions, economically7 advantageous radiation will invariably take place, and that beyond the cooler-end of span 63 useful radiation ability rapidly dies away in favour of flue-gas heat recovery'by convection and conduction. Having regard to the foregoing, itis desirable thatbeyond the cooler-end of zone 53 the conduit be equipped with one or more deector plates 54 (similar to that numbered 22 in Y Fig. 1) whereby the bulk of through-goingfluegas may be directed into close contact with the conduit walls. It may be further noted that vwhile the :presence of the deiiector plates 84 would appear` to impose a considerable obstruction of the flue-gas stream, such is not the case, because, with avertically disposed conduit such as 5l fluegases suffer a strong updraft, and as the gases leave the radiation zone 53 they are slow moving as a result of extensive heat loss (and consequent contraction) by radiation. A minor advantage due to the deector plates such as 54 is that they act as conductors (and as radiators) of heat to the adjacent portions of the conduit walls.

` Theconduit 5i' is surrounded by a'shell 55. The space betweenthe conduit and the shell constiu tutes va gas heating passage which at one end has a gas inlet box 56, and at its other end, a gas outlet-box 5l.

The conduit consists of a metal casing G8 and a refractory lining 59. The thickness and/or Com.- p'c'sitionof lining 59, and the extent ofY its intru- The ingy a conduit, an entrance end to said conduit adapted to receive flue gases exhausting from the flue-gas outlet of a furnace, an outlet end to' entrance Aend, a shell which closely surroundsA said conduit and therewith forms a Vgas heating passage, a gas inlet box which surrounds one end of said passage, a gas outlet box which surrounds the other end of said passage, means for feeding gas under pressure into said inlet box, means for conducting gas from said outlet'box, and outwardly iiared ends to said shell disposed inside and extending for a substantial distance within said boxes.

2. A combustion furnace recuperator comprising a conduit, an entrance end to said conduit adapted to receive ue gases exhausting from the flue-gas outlet of a furnace, an outlet end to said conduit communicating with the atmosphere, an unobstructed radiation Zone in said conduit havingy one end substantially coincident with said entrance end, a shell which. closely surrounds said conduit and therewith forms Va gas heating passage, a gas inlet box which surroundsl one end of said passage, a gas outlet box which surrounds the other end of said passage, means for feeding gas under pressure into said inlet box, means for conducting gas from said outlet box,` and thermal lagging means arranged externally of said shell and extending over a portion-only of said shell. A

3. vA combustion furnace recuperator compris'- ing a conduit, an entrance end to'said conduit adapted to receive nue gases exhausting from the flue-gas outlet ofV a furnace, an outlet end to said conduit communicating `with the atmosphere, an unobstructed radiation zone-inY said conduit having one end substantially coincident with said entrance end, a shell which closely surrounds said conduit and therewith forms agas heating passage, a gas inlet box which surroundsv one end of said passage, a gas outlet box which surrounds the other end of said passage, means forallowing differential expansion between said conduit and shell,` means for feeding gas under pressure into said inlet box, means for conducting gas from said outlet box, a feed pipe connected at one end to the inlet end of said conduit', pump devices for injecting cool air into the other end. of 'said pipe, a control valve associated with said feed pipe and link mechanism between the outlet end of the conduit and the control valve whereby the control valve is opened upon excessive expansion o f said conduit.

4. A combustion yfurnace recuperator comprising a conduit, an entrance end to'said conduit adapted to receive flue gases exhausting from the flue-gas outlet of a furnace, an outlet end to said conduit communicating with the atmosphere, an unobstructed radiation Zone in said conduit vhaving one end' substantially coincident with` said entrance .end, a shell which surrounds said conduit and therewith forms agas heating passage, a gas inlet box rwhich surrounds one end of said passage, a gas outlet box which surrounds the other end of said passage, means for feeding gas under pressure into .said inlet box, means for conducting gas from said outlet box, a 'feed pipe connected at one end to the inlet end of said conduit, pump devices for injecting cool air into the other end of said pipe, a spring loaded control valve in said feed pipe, and 'pull-rod' mechanism connected to operate said control valve in response to expansive movement of a part of the recuperator. 5.

5. A combustion furnace recuperator compris-1 ing a conduit, an entrance end to said conduit adapted to receive flue gases exhausting from the flue-gas outlet of a furnace, an unobstructed radiation zone in said conduit having one end substantiallycoincident with said entrance end, a shell which surrounds' said conduit and therewith forms a gas heating passage, a gas inlet box which surrounds one end of said passage, a gas outlet box which surrounds the other end of said passage, means for feeding gas under pressure into said inlet box, means for conducting gas from said outlet box, a jacket casing surrounding said shell open at one end to the atmosphere, a feed pipe connected to the other end of said jacket casing, pump devices for iniecting cool air into said feed pipe, and a control valve in said feed pipe'.y f

6. A combustion furnace recuperator comprising a conduit, an entrance' end to said conduit adapted to receive'fl'ue gases exhausting from the flue-gas outlet of a furnace, 'an unobstructed radiation zone in said' conduit having one end substantially coincident with 'said entrance end, a shell which-surrounds said conduit and therewith forms a gas heating passage, a gas' inlet box which surrounds one end of said passage, a gas outlet box which surrounds the other end of said passage, means 'for 'feeding gas under pressure into said inlet box, means' for conducting gas from said outlet box, a jacket casing surrounding said shellop'en at one end to the atmosphere, a feed pipe connected to the'other end of said jacket casing, pump devices for iniecting cool air into said feed pipe, a spring loaded control valve inV said feed pipe, and pull-'rod mechanism connected to operate said control valve inrresponse to expansive movement of a part'of the recuper-I ator.

'7. A combustion furnace recuperator comprising a rst recuperator section comprising a rst conduit, an entrance" end to said rst conduit adapted to receive `nue gases exhausting from the flue gasoutlet of a furnace, an outlet end' to said first conduit, an unobstructed radiation zone in said first conduit having one end substantially' coincident with said'entranc end, an unlagged shell surroundingl said rst conduit and therewith forming a gas heating passage, a gas inlet box surrounding 4one end of said passagea gas outlet b'ox surrounding the other' end of'saicl passage, a second recuperator section comprising a second conduit, an entrance to said second conduit connected to the outlet end of said rst conduit, an outlet end to said second conduit communicating with the atmosphere, an unobstructed 'radiation zone in said second conduit having one end substantially coincident with said entrance end 'to saidsecond conduit,` a lagged shell surrounding said second conduit andthere-- with forming; a gas heating passage,ja gas inlet box surrounding one-end ofsaid `last passage, a gas outlet box surrounding the otherend of said last passage, means for'feeding gas under pressure 'into said inlet boxes, and means for conducting gases from said'outlet boxes. f g

8. A combustion furnacerecuperator comprising a conduit, an entrance end to -said conduit adapted to receive flue gases exhausting fromthe flue-gas outlet of a furnace, an outlet end to said ,75 conduit communicating with the atmosphere, an

1 1 unobstructed radiation zone in said conduit having o ne .end substantiaily coincident with said entrance end, a shell which surrounds said conduit and therewith formsa gas heating passage, a gas inlet box which surrounds one end of said passage,

a gas outlet box which surrounds the other end of said passage, means for feeding gas under pres-` sure into said inlet box, means for conducting gas from said outlet box, thermal lagging means arranged externally ofv said shell and extending over a portion only of said shell, a flexible connection between the said inlet box and said shell,

a cooling trunk surrounding a -portion of said shell and which is open to the atmosphere, an air feed pipe connected to said trunk, a second air feed pipe in communication with the interior of said conduit, an air duct connected to both said feed pipes, means for iniecting cool air into said duct, a spring loaded control valvevin said duct, and pull-rod mechanismV to open said Valve in response to expansive movement ofl a part of said conduit.

9. A combustion furnace recuperator comprising a Vertical conduit, an entrance end to said conduit adapted to receive nue gases exhausting from the flue-gas outlet of a furnace, an outlet end to said conduit communicating with the atmosnhere, an unobstructed radiation zone in said conduit having one end substantially coincident with said entrance end, a shell which surrounds said conduit and therewith forms a gas heating passage, a gas inlet box which surrounds one end of said passage, a gas outlet box which surrounds the other end ofY said passage, means for feeding gas under pressure into caid .inlet box,

means for conducting gas from said outlet box, thermal lagging means arranged externally of said shell and extending over a portion only of said shell, meansfcr supporting said shellv and said conduit intermediately of their ends. a knifeedge sealing band at the bottom of said ccnduit, and a sand trough surrounding the said furnace outlet and into which the said sealing band dips.

10. A combustion furnace recuoerator comprising a downdraft recuperator section comprising a rst conduit, the upper end to said first conduit being connected to the flue gas outlet of a furnace, an outlet end at the bottom of said first conduit, an unobstructed radiation zone in said first conduit having one end substantially coinci.. dent with said uoper end, an unlagged shell surrounding said first conduit and therewith forming a gas heating passage, a gas inlet box surrounding one end of said passage, a gas outlet box surrounding the other end of said passage, an updraft recuperator section comprising a second conduit, an entrance end to said second conduit at 'the lower end of said conduit, an outlet end to said second conduit communicating with the atmosphere, an unobstructed radiation Zone inV said second conduit having one end substantially coincident with said entrance end to said second conduit, a Vlagged shell surrounding said -second conduit and therewthforming a gas Vheating passage, a'gas inlet box surrounding one end of said last passage, a gas outlet box surrounding theotlier end of said last passage, means for feeding gas under pressure into said inlet boxes, means for conducting gases from said outlet boxes, and an ashpit connecting the outlet end of said iirst conduit and the entrance end of said second conduit.

11. A combustion furnace recuperator comprising a conduit, an entrance end to said conduit adapted to receive flue gases exhausting from the flue-gas outlet of a furnace, an outlet end to said conduit communicating with the atmosphere, an unobstructed radiation zone in said conduit having one end substantially coincident with said entrance end, a shell which surrounds said conduit and therewith forms a gas heating passage, a gas inlet box which surrounds one end of said passage, a gas outlet vbox which surrounds the other end of said passage, means for feeding gas under pressure into said inlet box, means for conducting gas' from said outlet box, outwardly flared ends to said shell disposed inside said boxes, and thermal lagging means arranged externally of said shell and extending over a portion only of said shell.

12. A combustion furnace recuperator comprising a conduit, an entrance end to said conduit adapted to receive flue gases exhausting from the flue-gas outlet of a furnace, an outlet end to said conduit communicating with the atmosphere, an unobstructed radiation zone in said conduit having one end substantially coincident with said entrance end, a shell which surrounds said conduit and therewith forms a gas heating passage, a gas inlet box which surrounds one end of said passage, a gas outlet box which surrounds the other end of said passage, means for feeding gas under pressure into said inlet box, means for conducting gas from said outlet box, outwardly ared ends to said shellV disposed inside said boxes, thermal lagging means arranged external- 1y of said shell, and a plurality of fins attached to said conduit and extending into the said conduit between the radiation zone and the outlet end of said conduit.

13. A combustion furnace recuperator comprising a conduit, an entrance end to said conduit adapted to receive ue gases exhausting from the liuc-gas outlet of a furnace, an outlet end to said conduitl communicating with the atmosphere, an unobstructed radiation zone in said conduit having one end substantially coincident with said entrance end, a shell which surrounds said conduit and therewith forms a gas heating passage, a gas inlet box which surrounds one end of said passage, a gas outlet box which surrounds the other end of said passage, means for feeding gas under pressure into said inlet box, means for conducting gas from said outlet box, outwardly flared ends to said shell disposed inside said boxes, thermal lagging means arranged externally of said shell, a feed pipe connected at one end to the inlet end of said conduit, pump devices for injecting cool air into the other end of said pipe, and a control valve associated with said feed pipe.

14. A combustion furnace recuperator comprising a conduit, a shell which closely surrounds the conduit and therewith forms a gas heating passage, a gas inlet box which surrounds one end of saidpassage, a gas outlet box which surrounds thegother end of said passage, means for allowing diierential expansion between the conduit and shell, the ends of vsaid shell extending for a substantial distance inside said inlet and outlet boxes and being flared outwardly, and lagging means extend-ing externally over a part only of said shell.

15. A combustion furnace recuperator comprising a conduit, a shell which closely surrounds the conduit and therewith `forms la gas heating passage, a gas inlet box `which surrounds che 13 end of said passage, a gas outlet box which surrounds the other end of said passage, and a exible coupling between at least one of the inlet and outlet boxes and the said shell, a source o1 cool air, a feed pipe between the said source and the inlet end of the conduit, a control valve in the feed pipe, and pull-rod mechanism between the outlet end of the conduit and the control valve to open the control valve upon excessive expansion of the conduit.

16. A combustion furnace recuperator comprising a conduit, a shell which closely surrounds the conduit and therewith forms a gas heating passage, a gas inlet box which surrounds one end of said passage, a gas outlet box which surrounds the other end of said passage, the ends of said shell extending for a substantial distance inside said inlet and outlet boxes and being ared outwardly.

HANS ESCI-IER.

REFERENCES CITED The following references are of record in the le of this 1patent:

UNITED STATES PATENTS Australia Sept. 5, 1928 

